Information surfaces are to be found among displays shields to show certain pictures, symbols and texts. The invention regards all dimensions larger than microscopic and for use inside and outside.
With the technique of today, displays, as signboards, television and computer screens, can be used for showing one image at a time only. The word xe2x80x9cimagexe2x80x9d will in this text be used in the meaning image, symbol, text or combinations thereof. An obvious drawback of any display presently available is that when viewed from a small angle, the image appears squeezed from the sides. This deformation increases as the viewing angle becomes smaller, this is an obvious oblique viewing problem.
When using printing equipment with high resolution, an image can hold more information than the eye can detect. It is possible to compare the phenomena with a television screen. At a close look it is seen that an image here is represented by a large number of colored dots, between the dots there are information-free grey space. The directional display has such information-free space filled with information representing other images. The background illumination bring these images to appear when viewed from appropriate viewing angles.
Essentially, the ratio of the printing resolution to the resolution of the human eye under specific viewing circumstances gives an upper bound for the number of different images which can be stored in one image. This is true for the directional display in the so called one-dimensional version. In the two-dimensional version, an upper limit on the number of images is the square of that ratio. The viewer getting further from the display is clearly a circumstance which decreases the resolution of the eye with respect to the image. Hence, images intended for viewing at a long distances may in general contain more images. If the printing resolution comes close to the wavelength of the visible light, diffraction phenomena becomes noticeable. Then an absolute bound is reached for the purpose of this invention.
The resolution ratio of the printing system and the eye bounds the number of images that can be represented in a multi-image, this is also a formulation of the necessary choice between quantity of images and sharpness of images. The limits of the techniques are challenged when attempting to construct a directional display which shows many images with high resolution intended for viewing at close distance.
Directional displays are always illuminated. The one-dimensional directional display shows different images when the observer is moving horizontally, when moving vertically no new images appear. The two-dimensional display shows new images also when the viewer moves vertically. In this text we will mainly describe the one-dimensional version. A directional display can be realized in a plane, cylindrical of spherical form. Other forms are possible, however from a functional point of view equivalent to one of the three mentioned. The plane directional display has usually the same form as a conventional lighted display. The cylindrical version is shaped as a cylinder or a part of a cylinder, the curved part contains the images and is to be viewed. The spherical directional display can show different images when viewed from all directions if it is realized as a whole sphere.
The plane display has a lower production cost than the cylindrical and the spherical versions. Sometimes this version is easier to place, however it has the obvious drawback of a limited observation angle. This angle is however larger than a conventional flat display because of the possible compensation for the oblique observation problem. The cylindrical display can be made for any observation angle interval up to 360 degrees.
Showing different messages in different directions is practical in many cases. A simple example is a shop at a street having a display with the name of the shop and an arrow pointing towards the entrance of the shop. Here the arrow may point towards the entrance when viewed from any direction, which means that the arrow points to the left from one direction and to the right from the other one. The arrow can point right downwards from the other side of the street, and change continuously between the mentioned directions. Furthermore, the name of the shop can be equally visible from any angle.
A lighthouse can show the text xe2x80x9cNORTHxe2x80x9d when viewed from south, xe2x80x9cNORTHWESTxe2x80x9d when viewed from southeast, and so on. Unforeseeable artistic possibilities open. For example, a shop selling sport goods can have a display where various balls appear to jump in front of the name as a viewer passes by. The colour of the leaves of trees can change from green to yellow and red, as to show the passage of the seasons.
Another use of the directional display is to show realistic three-dimensional illusions. This is achieved simply by in each direction showing the projection of the three-dimensional object which corresponds to that direction. These projections are of course two-dimensional images. The illusion is real in the sense that objects can be viewed from one angle which from another are completely obscured since they are xe2x80x9cbehindxe2x80x9d other objects. Compared to holograms, the directional display has the advantages that it can with no difficulties be made in large size, it can show colours in a realistic way, and the production costs are lower. Three dimensional effects and moving or transforming images can be combined without limit.
The oblique viewing problem disappears if the directional display is made in order to show the same image in all directions. In this case, for each viewer simultaneously it appears as if the display is directed straight towards him/her.
Examples of environments where many different viewing angles occur are shopping malls, railway stations, traffic surroundings, harbours and urban environments in general. One can show exactly the same image from all viewing angles with a cylindrical display on a building as shown in FIG. 1 shown in the appendix regarding the drawings.
Basic Idea
The directional display is always illuminatedxe2x80x94either by electric light or sunlight. The surface of the display consists on the inside of several thin slits, each leaving a thin streak of light. The light goes in all directions from the slits. On the outside, in front of all slits, there is a strongly compressed and deformed transparent image. A viewer will only see the part of the images which is lighted by the light streaks. If the images are chosen appropriately, the shining lines will form an intended picture. If the viewer moves, other parts of the images printed on the outer surface will get highlighted, showing another image. The shining lines are so close together so that the human eye cannot distinguish the lines, but interprets the result as one sharp picture.
The two-dimensional version has small round transparent apertures A instead of slits S. Analogously, the viewer will see a set of small glowing dots of different colors. Similar to a TV-screen, this will form a picture if the dimensions and the colors of the dots are chosen appropriately. The rays will here highlight a spot on the outside. The set of rays which hit the viewer will change if the viewer moves in any direction.